In recent years, there is strongly required a cooling mechanism of which the size and thickness have been reduced and which is efficiently used to cool heat-generating components (components to be cooled), such as semiconductor elements (CPU, GPU, and the like) mounted in a housing, of which the size and the thickness have been reduced and the performance have been improved, of a tablet, a smartphone, a notebook PC, or the like. There is a heat pipe as one of typical cooling mechanisms.
The heat pipe is a vessel (container) such as a metal pipe that is vacuum-degassed and hermetically sealed and where condensable fluid serving as working fluid is sealed. The heat pipe automatically operates when a temperature difference occurs in the heat pipe. Working fluid, which is vaporized at a high-temperature portion (heat source side), flows to a low-temperature portion (heat-radiating side), radiates heat, and is condensed. Accordingly, the heat pipe transports heat in the form of the latent heat of the working fluid.
That is, a space, which serves as a flow passage for working fluid, is formed in the heat pipe, and working fluid received in the space is subjected to a phase change, such as vaporization or condensation, or is moved. As a result, heat is transferred. Working fluid is vaporized on the heat source side of the heat pipe by heat that is generated by components to be cooled and is transferred through the material of the container forming the heat pipe, and the vapor of the working fluid moves to the heat-radiating side of the heat pipe. The vapor of the working fluid is cooled on the heat-radiating side, and returns to a liquid-phase state again. The working fluid, which has returned to a liquid-phase state in this way, moves (returns) to the heat source side again. Heat is transferred by a phase change or the movement of the working fluid.
As the heat pipe, there are a round pipe-shaped heat pipe, a sheet-shaped heat pipe, and the like in terms of the shape of the heat pipe. A sheet-shaped heat pipe is suitably used to cool a heat-generating component that is mounted in a housing, of which the size and the thickness have been reduced and the performance have been improved, of a tablet, a smartphone, a notebook PC, or the like. The reason for this is that a sheet-shaped heat pipe is easily mounted on a heat-generating component and has a large contact surface.
A sheet-shaped heat pipe in the related art is a sheet-shaped heat pipe 900 of which the surface of a container 911 is flat as illustrated in FIGS. 14A and 14B. Meanwhile, FIGS. 14A and 14B are diagrams illustrating a heat pipe 900 that is an example of a sheet-shaped heat pipe in the related art. FIG. 14A is a schematic perspective view of the heat pipe 900, and FIG. 14B is a schematic cross-sectional view of the heat pipe 900 taken along line A-A illustrated in FIG. 14A. As illustrated in FIGS. 14A and 14B, the heat pipe 900 in the related art includes the container 911 of which peripheral portions of sheet-shaped members 911a and 911b disposed so as to face each other are joined to each other so that a hollow portion is formed in the container 911. The hollow portion of the container 911 includes wick-occupied portions 913 that are occupied by wick structures 913a stored and disposed in the container 911 and space portions 912 that are not occupied by the wick structures 913a. 
Further, as another example of the sheet-shaped heat pipe of which the surface of the container in the related art is flat, there is a sheet-shaped heat pipe of which the surface of a container including a metal flat plate and a metal flat plate for a cover disposed so as to face each other is flat. This heat pipe is a planar heat pipe in which a variant cross-sectional groove including a shallow groove portion and a deep groove portion is formed at a metal flat plate portion serving as the inside of the container, the deep groove portion serves as a vapor flow passage, and the shallow groove portion serves as a fluid flow passage so that a small thickness and a large contact area can be obtained (Patent Document 1).